Tattoo Sensor as Needleless Glucose Monitor for Diabetic Patients

Researchers at the University of California San Diego Jacobs School of Engineering are in the process of creating a needleless glucose monitor nicknamed the tattoo sensor. After being diagnosed with diabetes, Angela Valdez made adjustments to her diet and physical activity. She assumed she was doing everything right.

Dr. Edward Chao is the principal investigator of a phase I clinical trial testing the accuracy of a needleless glucose monitor developed by University of California San Diego Jacobs School of Engineering researchers that adheres to the skin like a temporary tattoo to read blood sugar levels. (Image credit: UC San Diego Health)

I don't handle monitoring my diabetes as I should. I have the diet down a lot better now and I take my medication as I should, but the finger pricking is a struggle for me. I only test if I feel bad. If I don't feel my blood sugar level is high, and I'm taking the pill every day, I think I'm alright. Which is really bad thinking, but the pinprick is terrifying.

Angela Valdez

Valdez is one of 29 million people living with diabetes in the United States for whom monitoring their blood sugar level is an integral component of handling their condition. Understanding how a patient's sugar levels rise and fall over the course of time can guide medication routines, and alterations can be recommended to enhance quality of life, possibly even save it.

Unfortunately, like Valdez, numerous patients with diabetes do not monitor their blood glucose regularly. According to Edward Chao, DO, associate clinical professor of medicine at University of California San Diego School of Medicine and a physician at VA San Diego Healthcare System, one-quarter of persons who are on insulin treatment rarely or never test their blood sugar levels. Another 65% of patients who use other diabetes drugs test merely once a month or less.

Adherence to chronic disease management is low - about 50 percent. Diabetes is no exception. There's more self-management involved in diabetes, including using needles to test blood glucose, monitoring foot health, managing medications and keeping regular clinical appointments. That's a lot more than many other conditions. We need to introduce a tool that reduces discomfort or inconvenience to increase vital monitoring of glucose.

Edward Chao

A new needleless glucose monitor nicknamed the tattoo sensor has been developed, which can measure insulin levels through sweat on the skin. This endeavor was realized by UC San Diego Jacobs School of Engineering researchers, led by UC San Diego Center for Wearable Sensors director Joseph Wang, DSc, SAIC Endowed Chair of Engineering, and co-director, Patrick Mercier, PhD. This glucose monitoring patch eliminates the prick factor.

"Just like a kid's temporary tattoo, you apply it on the arm, dab with water and remove the back paper," said Mercier, an assistant professor in the Department of Electrical and Computer Engineering. "Our tattoo, however, is printed with material containing two electrodes that apply a small amount of electrical current. This forces glucose molecules that reside below the skin to rise to the surface, allowing us to measure blood sugar. It's safe and you can't really feel it."

Valdez has registered in a phase I clinical trial headed by Chao, in partnership with Wang and Mercier. The ENGAGE Study is happening at UC San Diego Altman Clinical and Translational Research Institute, where the team tests the accuracy of the tattoo sensor at detecting glucose levels compared to an old-style glucometer.

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Participants are required to wear a sensor during fasting, at different times up to a couple of hours after eating. To confirm accuracy, glucose levels from the sensor will be compared to results from concurrent finger stick glucose readings.

"They placed the sensor on my shoulder and I washed it and dried it," said Valdez. "They said I should feel a mild sensation when they plugged in the electronic glucose monitor. I didn't. At one point it felt like a bug landed on me, but it was barely noticeable. After the first round I took a break to eat and work at my desk for a short time. I functioned like I normally do. I went back for the second round and didn't feel any discomfort. I can see wearing it all day."

The clinical trial is signing up 50 adults, ages 18 to 75, with either type 1 or 2 diabetes or diabetes because of other causes. Type 2 diabetes occurs when the body cannot create or becomes resistant to insulin—the master regulator of glucose storage and use. Type 1 diabetes is an autoimmune disease that terminates insulin-secreting beta cells in the pancreas, leaving the body incapable of creating insulin.

By making a noninvasive, discrete, and user-friendly product that is economical, the UC San Diego team hopes to remove barriers that deter patients from testing blood sugar levels regularly. If manufactured on a large scale, Mercier believes the tattoos could be priced in the same way to what glucose test strips cost presently, approximately $1 per single-use strip.

In its present stage, the tattoo sensor gives a single readout. In due course, Mercier hopes to have a continuous sensor that tracks glucose for an entire day.

There are continuous glucose monitors on the market. However, the technology still necessitates injecting a needle into the abdomen every few days to measure glucose through interstitial fluid and requires calibrating with finger sticks intermittently.

"Drawing blood is uncomfortable. No one likes doing it. The beauty of the technology we are developing is that it is a truly noninvasive means to measure glucose," said Mercier. "The main purpose of our research is to develop new technologies that can monitor glucose without drawing blood and ideally measure it over the course of the day. By giving this real-time information to patients, they can manage their consumption of sugars and injections of insulin much better than with periodic spot measurements."

Presently, to obtain the most up-to-date data, patients prick their fingers a few times daily. Blood is then applied to a glucose test strip which is placed into a portable glucometer for analysis of glucose levels. The data collected, however, is still limited. To get a better idea of a patient's total health more frequent testing — or better yet, continuous tracking — provides a fuller, more comprehensive picture of what is taking place inside the patient's body when he or she is active or eats, said Chao.

"Even if you are not on insulin, it's useful to have a glucometer in times of rapidly changing glucose levels," said Chao. "We're not just trying to prevent dangerous highs and lows. That's the immediate feedback. In the long term, this allows us to discern patterns throughout the day when a person is running really high or having trouble spots when they're running hypoglycemic."

Hypoglycemia, or abnormally low blood sugar, can be risky and necessitates immediate treatment. A severe case might cause a person to be unable to treat themselves and could result in seizures or even death. Diabetes has been identified as the seventh leading cause of death in the U.S.

Hyperglycemia (high glucose levels) occurs when the body has very little insulin or is not utilizing insulin properly to regulate blood sugar. If untreated, hyperglycemia poses greater long-term consequences, including a condition known as ketoacidosis (diabetic coma). Hyperglycemia can also raise a person's risk of diabetic complications, such as stroke, peripheral atrial disease, heart attack, kidney disease, blindness, and more.

There are times when people will notice that when their glucose is low. They may feel sweaty, shaky or irritable. But, some people may not recognize when they have hypoglycemia. People with high blood sugar may not feel any different and won't know they are running high. That's scary. That's where having a continuous glucose monitor will be very useful and lifesaving.